The CData ADO.NET Provider for Kintone supports standard SQL joins like the following examples.

Inner Join

An inner join selects only rows from both tables that match the join condition:

SELECT Apps.Name, Comments.Text FROM Apps INNER JOIN Comments ON Apps.AppId = Comments.AppId WHERE Comments.Appid=5 AND Comments.RecordId=1

Left Join

A left join selects all rows in the FROM table and only matching rows in the JOIN table:

SELECT Apps.Name, Comments.Text FROM Apps LEFT JOIN Comments ON Apps.AppId = Comments.AppId WHERE Comments.Appid=5 AND Comments.RecordId=1